Renewable cartridge fuse



W. .J` PFLAUN RENEWABLE CARTRIDGE FUSE Sept. 5, 1950 Filed June 5, 1947 INVENTOR.

Patented Sept. 5, 1950 UNITED STATES PATENT OFFICE RENEWABLE CARTRIDGEFUSE William J. Psaum, Pittsburgh, Pa. Application June 1947, Serial No. 752,7 83

This invention pertains to cartridge fuses and especially to such in which a fusible member is contained in a renewable unit.

-Electric fuses of this type are carried by resilient contactors or clips holding the two knife blades of the fuse snugly, intended to vcontact substantially the whole of the fiat side surfaces vthereof for causing the least resistance to the flow of the electric current. As the knife clips are mounted on blocks and lined up so that kthe corresponding operative clip surfaces are Ain the same plane it is of utmost importance that the knife blades of the fuses be perfectly alined and securely held because only in such a case will the fiat operative surfaces of the knives contact on their entire area the knife clips and secure thus best electrical conduction` with the least heat development and loss of energy. As the two knife blades vare separate pieces mounted to an insulating bridge bar and electrically connected by a fusible conductor, the wholev being carried by an insulating casing, the proper alinement of the two knife blades can be achieved onlyby employing structures that attach all parts of the fuse mechanically rigidly together and prevent the development of excessive stresses which could cause damage to the casing ofthe fuse or to its bridge bar portion when' the fusible part is burnedv out by an electrical overload.

The fuses known up to date did notestablish such optimum conditions because they permitted relative displacement between the parts of the fuse in case of variations in their temperatures, hence they did not fully prevent the knife blades from getting out of alignment or becoming distorted and thus from losing efficiency under exacting operating conditions. o y

My invention obviates these and other disadvantages by providing a fuse in which all stressed parts are mechanically rigidly connected to each other and which is so constructed that itt prevents the development of excessive stresses in the non-fusible parts even in case that the fusible part is burned out by an electrical overload.

I-Ience oneof the objects of my invention is to provide a renewable cartridge fuse the coacting parts of which are mechanically rigidly connected to each other.

Another object of the invention is to create a renewable cartridge fuse in which the cooperat-r` gasfpa'ssages Aof peripheral annular cross section:L

6 Claims. (C1. 20o-131) al areas with relatively large bounding surfaces.

Still another object of the invention is to provide a device of the character described in which the knife blades are axially and angularly rigidly connected to the insulating bridge and to the insulating casing as well, by attachment means and connector means, respectively, that prevent any relative displacement axially, laterally or angularly between the parts by positive interference.

Another object of the invention is to provide a renewable fuse in which the linear, thermal expansion or contraction of the casing and of the portion of the renewable unit which is within the casing, is substantially the same.

Yet' another object of the invention is to provide a renewable cartridge fuse which employs minute clearances of tortuous configurations for ventilation of the internal cavity of the casing for preventingthe occurrence of excessive gas pressure, within the casing.

Another object of the invention is to provide a renewable cartridge fuse the internal cavity of which communicates with the atmosphere through minute passages of tortuous configurations and of relatively substantial lengths formed by mechanically rigidly connected metallic parts through which gases, generated within the casing by an electrical overload, will escape to the atmosphere at permissible pressure and cooled to a permissible temperature.

A further object of the invention is to provide a renewable fuse which has an improved electrical connection between the knife blades and the fusible element whereby the electrical resistance and with it the production of heat and waste of energy are substantially decreased.

Another object of the invention is to provide a device of the type set forth in which the attachment Ameans between insulating bridge, knife blades .and fusible element include a channel member having a web portion and flanges extending perpendicularly therefrom inboth directions snugly eznbracing.4 the side, topand bottom surfaces of the flat bar-shaped knife blades and thoseof the insulating bridge bar and also include an axially grooved cylindrical member with threaded extensions of reduced diameter at both ends thereof pressed through and peened into the knife bladesland the channel members and be-A ing provided -on each extension with a suitable nut for rigidly attaching the fusible member and the bridge bar, respectively, to the knife blades.

Yetanother object of the invention is to provide a renewablecartridge fuse in which the insulating casing is subjected to a predetermined tensile force and the insulating bridge bar to an equal compressive force, the latter being the reaction of the former and the structure is such that temperature variations will not substantially affect these forces which remain substantially constant under all thermal conditions.

Further objects of this invention are to provide a device of the class set forth which is simple in its construction and arrangement, durable and eiiicient in its use and inexpensive to manufacture.

The accomplishment of these and other objects by my invention will be clearly evident to. those versed in the art when reading the following specification and perusing the accompany'- ing drawing in which:

Figure 1 is a fragmentary, longitudinal crosssectional View of the device in accordance with.

my invention, shown partly in outline.

Figure 2 is a radial cross sectional view on line 2-2 in Figure 1.

Figure 3 is a side elevational view. of theknife blades and their connecting parts detached from the casing.

Figure 4 is an explodedview of the knife blade assembly shown in Figure.

Figure 5 is a perspective view of a inodied form of the studas used in Figures l to 4.

Figure 6 is a fragmentary sectional View of the knife blade assembly, partly in outline,show ing the stud shown in Figure 5 in position.

Figure '7 is a perspective view of one of the terminal discs as usedA in this invention.

Figure 8 is a, perspective view, slightly reduced, of one of the knife blade endsshowing; the channel member andthe inner, rdisc. securely held in position on the knife blade by. a stud..

Referring now to the drawingy and` especially to Figures 1 to 6 inclusive, illustrating. the preferred embodiment, I represents a tubular casing of electrically non conductive material (such as hard fibre or other suitable material) to. which ferrules II, one at each end, of. the casing, are rigidly attached by means of. rivets. I 2, shown, or otherwise. Ferrules ILI have threaded end portions i 3 upon which preferably ring-shaped cap-nuts. I4 are screwed'. These cap-nutsY I4. are for hand operation for which purpose their outer cylindrical surfaces are knurled. Cap-nuts I4 are also provided with an endbore I5. an adjoining cylindrical inner portion of greater diameter IS, and an internal' threaded' portion I1 that coacts with threaded end. portion I3' offerrules I I.

I8 represents a terminal' disc which. loosely fits in bore I6 of cap-nut I4 and is retained' therein by the shoulder 2I formed: between the smaller end bore I and the'largercylindrical inner portion I6.

Each terminal disc I 8 is provided with an elongated aperture I9 (see Figure 7) which slidingly ts the knife bladethat protrudes outwardly through it. Each of said knife bladesA 2U has a shoulder 22 inwardof which the knifeA` blade is narrowed forming tang 23. In alignment with shoulder 22 is inner disc 25 which has a suitable elongated aperture for snuglyV admitting the tang 23 of knife blade 20.

It will be noted that the end portion 24 of channel member 21, when secured in position by driving the uted stud 28 through the prepared apertures through the narrow portion 23e of knife blade 20 and said channel member 21', will force the inner disc againstthe shoulder 22 of the knife blade 20 and thuszretainthe innerk 4 disc 25 in fixed position without peening blade 23 around aperture of disc 25, which is usually done.

Tightly abutting the disks 25 is a bridge bar 2E which may be preferably from the same electrically insulating material as casing I0 or from a different one which, however, has substantially the same coefficient of thermal expansion. Between the tangs 23 of knife blades 20 and bridge bar 26 is the channel member 21 having a web portibn33= andperpendicularly thereto flange portionsy v34 which extend therefromv iny both directions and hug snugly tang 23 on one side and bridge 26 on the other at their respective wide and narrow side surfaces.

Web 33 of channel member 21 is provided at itscenter with hole 4I of suitable diameter that coacts with properly located similar hole 42 in the tang to receive grooved portion of stud 28 that. is. pressed into Aboth holes. Holes 4I and 42 have somewhat smaller diameter than the edges or teeth-formed by the grooves so that the latter penetrate. into the material surrounding the holes and an electrically and mechanically intimate connection results between. stud. tang and channel member positively resisting relative angular displacement therebetween. It will be noted that flange portions 34 are symmetrical to the longitudinal and transversal cross sectional central planes of the. web intersecting at the center of hole 4I` The result of this symmetrical arrangement is that the flanges contact the tang and bridge bar at the same distance on both sides of stud 28resisting. most effectively rotary forces. Hence the connection` by each-stud and channel member makesy thestructure rigidY without relying on theother stud andother channel member; furthermore the web 33 being abutted over its entire area. by the adjoining tangA the web is relieved from .bending stresses.

Thev above mentioned, grooved studs` 28 have a cylindrical middle. portion 35 of relatively large diameter provided, withy axially running grooves l36 and having. at. both.l ends threadedV axial extensions of reduced. diameter indicated` by the numeral 29., coacting withy nuts y3l). After the cylindrical middle portion 3.5- of. stud 28, is pressed through tang 23. and through channel member 21. it isv peened from bothsides forming an an,- nular peening groove 3E. and the corresponding outwardly conical enlargement of the grooved cylinder rigidly connecting tang 23 and. channel member 21 and through extensions 28 and nuts 30. also bridge bar 26 which are thus transformed into a rigid unit, Mounting washers 3l,4 fuse link 32v on extensions 29 and` tightening nutsl 30', a rigid mechanical;- and excellent electrical connection is established between. the. two spaced apart knife blades 20: The inner. disc 25, rigidly held against the shoulderz22 of knife blade 20 by the4 channel member 21, completes the rigid renewableunit the'axiallengthof which between the inner discs is` denoted -by'C.

At this time I wish to mention that .one `of. the main features of my invention is the methodof. assembling the channelmember 21. to the tang 23 of the'knife blade 20, so that saidchannel member 21'Y also. retains rigidly the inner disc 25 against the shoulder 22of;the knife. blade 20,2411 by means of the grooved stud 28` providedV with threaded extensions 29, Vthe, latter ofwhich serving to securely holdv one end of. the fuse link 32 andone end ofthe bridge bar 2B by nuts 30. In

other words, the grooved studs 28 serve aV triple purpose; first, Jtopermanentlysecure` the channelrmember 21- to' tang y23joufjkni1'e'blade 20.; second"l to `permanently and securely-'retain the inner disci-'25` against theshoulder 22 of kniieblade ,-28

lwithout .peening the. tang as is conventionally done y.and third, to vremovably fasten the bridge 26 As it is shown in figure .1 thev axial length lofthe casing |01 including the attached ferrules II is denoted 'by B which is somewhat lessv than C. It

vwill be also noted that the length of the threaded portion I3 of ferrule II is greater than that .of the inner threaded portion I1 yof cap-nuts I4. Consequentlyv mounting the assembled renewable unit and terminal discs I8 is the casing by screw.-

iingcap-nuts I4 upon ferrule I I vthere will be a gap between each ferrule and cap-nut and the screws will tend to elongate the casingIIl imparting toit through rivets I2 a predetermined tensile force acting axially. The same time bridge 26 ,y will be compressed through discs I8 and 25 by. force equal to -that which tensions casing I0 as the lformer force is the reaction of the latter and the whole fuse is held axially and radially rigidly together as a unit or as one piece.

The device operates as follows:

, The renewable unit having axial length C and bounded by inner discs 25 from which knife blades 28 protrude exactly aligned in both directions, is inserted into casing I8 upon which ferrules II vare mounted rigidly. The discs 25 slidingly loosely engaged the inner surface of ferrules II and aline the renewable unit coaxially in the casing I0. Discs 25 will somewhat protrude from .ferrules I I and they are preferably so set thatthe protrusions should be equal on both sides amounting to however an unequal distribution of the protrusions will do no harm. Terminal discs I8 'are nowy slipped over the knife blades 20 into contact with inner discs 25 and finally cap-nuts I4 are screwedonthe threaded portion I3 of ferrules I I suiciently tight to complete the assembly to one rgidunit. v f

It will be noted that the length A of the casing between the rivets I2 is approximately equal with that of the bridge portion extending between the centers of the iluted studs 28, furthermore, that `the length D of the peripherie metallic Parts .(ferrule II and cap-nut I4 measured from rivets I2 to theend of disk 25) is approximately equal jwith that of the knife yblade portion between shoulder 22 and the center of stud 28. As the metallic parts and insulator parts on the casing `.as well as in the central renewable portion of the fuse` have the same axial length and substantially the same coeflicients of thermal expansion vthere will `be no relative displacement or distortion because O f change of temperature dueto electrical overload, burning out of the fuse' and possiblearc formation, as the fuse will axially elonn gate and contract respectively as one whole 4.piece in response ,to temperature variations.

" The'gases developing from combustion and arc formation will pass into the atmosphere exclusively through the tortuous path of minute widths f constitutedfby the small clearances of the sliding v.relativelylong path `of internal pressure relief,

are all metallic, hence the escaping gaseswill `be effectively cooled and an ignition by them ofvcomrbustible matter outside of the fuse casing will be prevented. Hence the initial axially and radially lrigid mounting of all the parts of the'fuse will be maintained throughout, due to the avoidancerof relative'displacement between the casing andrenewable unit, consequently the knife blades will not be thrown out of their exact alignment but will always Contact the clips or prongs by which they are held on their full contact areas. Asa result, the effectiveness of thefuse will 'be maintained and an increase of resistance, overheating and waste of electrical energy avoided.

Figures 5 and 6 show a second embodiment of my invention Which is substantially the same as the rst embodiment with the exception that a greater air space 3l between the fuse link 32r and the bridge bar 26 is created (Figure 6) by providing a reduced extension 38 at one end of the grooved portion of the stud 39 as shown in Fig. 5.

In order to replace the fusible link 32 it is only required to unscrew `one of the cap-nuts from casing I8, after which the complete fuse assembly may be withdrawn. Subsequently the nuts 38, which hold the fuse in position, are loosened enough to releasethe ends of the fusible link and a new'one is slipped around the threaded extensions 29 of studs 28 or 39 and the nuts are tightened'again.

Inv some cases, it is necessary to replace the bridge Vbar 26, this being readily accomplished by removing the nuts 38 from the threaded stud extensions 29,.=after which the new bridge bar with stud and channel member is put in place and fastened with the nuts 38.

Since one of the cap-nuts I4 and oneof the terminal discs I8 have not been removed from theV casing while replacing a new fusible link 32 it is now only required to insert one of the knife `blade ends 28 of the removable fuse link assembly through the elongated slot I9 of said terminal disc I8 `after which the other terminal disc I8 is slipped over the free end of the knife blade assembly and the cap-nut I4 is again screwed home into its normal position.

No tools other than a wrench or a pair of pliers are required to replace a fuse in the device.

From the above description it will be seen that each of the knives is part of a compact unseparable unit, that is, the knife blade 28, the channel member 2l, the inner disc 25 and the grooved stud 28er 3 9.` vThe separable parts in the fusible linkiassembly are the fusible link, the bridge bar, .andqof course, lthe nuts which hold the link and the bridge in position.

Having fully described my invention and illustratedpreferred embodiments thereof it will be understood that various changes and modifications maybe made in the combined structures `llletters Patent is:4

m1. A. cartridge fuse comprising an electrically insulating tubular casing, attachment meansr for `detachably but rigidly connecting thereto a reynewable fuse unit composed oftwo, shouldered, outwardly wider knife blades extending axially in ,oppositey directions from said casing symmetricallydisposed toIan-axial central plane thereof, an elongated ,bridge ,bar of f electrical insulating materiel: ererlapririsln.separating said blades@ metallic link fusible `by predetermined'electrical overload connecting said knife blades, a metallic inner disc seated against the shoulder of each of said blades, a metallic terminal disc seated on each of said blades between said inner vdiscs and said attachment means, metallic connector means rigidly fixing said knife blades to said bridge bar and retaining said fusible link, said connector means for each of said blades including a stud having an axially grooved cylindrical body and threaded extensions with nuts thereon, a channel member having a web with a `centrally located hole for seating said grooved body and ange :portions protruding perpendicularly from said web which is adapted to be interposed between the overlapping portions of said bridge bar and blade snugly clamping them, whereby said connector means prevent angular displacement between said bridge bar and said blade without subjecting said web to bending.

2. A cartridge fuse comprising an electrically insulating tubular casing, attachment means for detachably but rigidly connecting thereto a renewable fuse unit composed of two, shouldered outwardly wider knife blades extending axially in opposite directions from said casing symmetrically disposed to an axial-central ,plane thereof, an elongated bridge bar of electrically insulating material overlappingly separating said blades, a metallic link fusible by vpredetermined electrical overload connecting said knife blades, a metallic inner disc seated against the shoulders of each of said knife blades, a. metallic terminal disc seated on each of said blades between said inner discs and said attachment means, metallic connector means rigidly fixing said knife blades to said bridge bar and retaining said 'fusible link, said connector-means for each of said blades compris-ing a stud having an` axially grooved 'cylindrical lbody and threaded extensions withnuts thereon, a channel memberl'with a quadrangular 'web vcarrying a centrally located hole coacting with suitable holes insaid bridge bar and said blade for forcefse'atin'g 'the :grooved body in said blade and 'web and flanged .portions protruding perpendicularly'onboth sides of ysaid web which is adapted to be interposed in its entirely between `the overlapping por-tions of said bridge bar and blade so the web and the flanges contac't snugly `one side and Vat least -one edge of each of said bar and said blade, 'whereby angular displacement between -said brige bar and said blade is -prevented without-subjecting said web tobending 3. A cartridge fuse comprising an electrically insulating tubular casing, attachment meansfor -detachably but rigidlyconnecting thereto aref newable fuse unit composed of two shouldered outwardly wider knife blades extending axially in opposite directions from said casing symmetrie cially disposed to 'an axial central plane thereof, an elongated bridge bar of electrically insulating materialoverlappingly separating said blades, a metallic link fusible by predetermined electrical overload connecting said knife blades, la metallic inner ldisc having a central aperture corresponding to the cross-section of the narrower portion of Vsaid blades seatedagainst the shoulder of each of said blades, a `metallic terminal disc having va central aperture corresponding to the cross-secition of `the Iwider portion of said blades seated on each of said .blades between said inner discs 'and said attachment means, 'metallic connector means rigidly connecting said knife lblades k'to said bridge bar and retaining said fusiblelink said connector` lmeans for'each` -ofsaid blades comprising a stud having an axially grooved-UY- lindrical body andthreadedextensions with nuts thereon, a channel member having a quadrangular web `carrying a centrallylocated hole coacting with corresponding holes in the bridge bar and blade for force-seating the groovedbody in said blade and web, nange portions on opposite sides'of the web extending substantially perpendicular vto the plane of the web, said channel lmember being adapted to be interposed between the overlapping portions of the bridge bar and blade, said web being in contact over substantially its entire surfaces with the blade `and bar and said ilange portions being in contact with the edges of said .barsand blade whereby the-connector means prevent angular displacement between said bridge bar and said blade without subjecting said web to bending. f

4. A cartridge fuse comprising an electrically insulating tubular casing, attachment means including a ferrule rigidly fixed to each end portion of said casing for detachably but rigidly connecting thereto a renewable fuse unit composed of two shouldered outwardly wider knife blades extending axially in opposite directions from said casing symmetrically disposed to an axial central plane thereof, an elongated bridge bar of electrically insulating material overlappingly separating said blades, a metallic link fusible .by predetermined electrical overload connecting said blades, a metallic inner disc having a central aperture corresponding to the cross-section of the narrow portion of said blades seated against the shoulder of each 'of said blades, a metallic terminal disc having a central aperture corresponding to the cross-section of the wider portion of said blades seatedon each of said blades between said inner disc and said attachment means, metallic connector means rigidly connecting said knife blades to said 'bridge bar andretaining said fusible link, said connector means for each of said blades comprising a stud having an axially grooved cylindrical body and threaded extensions with nuts thereon, a channel member having a quadrangular web portion carrying a centrally locatedhole coacting with corresponding holes in said bridge bar and blade for forceseating the grooved cylindrical 'stud body in said blade and web, symmetrically placed flange portions extending perpendicular to the body plane of the web on opposite sides thereof, said channel member being adapted to be interposed between the `overlapping portions of said bridge bar and blade, said web portion being in -contact with the bar and blade over substantially all of yits surfaces and said flange members abutting the edges vof the bridge bar and blade in tight engagement therewith whereby said connector means :prevent angular displacement "between said bridge bar and blade without subjecting said web to bending, said casing and ferrule on one hand and said 'component parts of said renewable rfuse uniton the other hand having such axial dimensions'and being made of such material that their thermal expansions atvarying temperatures `are relatively the same, whereby relative heat distortion between them is avoided incident to temperature variations said discs, blades, and attachment vmeans forming with each other minute 'passages for rthe escape and cooling of gaseous 'matterexpanding from the internal cavity of said 'casing to the atmosphere. 4

5. A cartridgefusetaccording toclaima in which said grooved cylindrical bodies.V after forced insertion into `said blades lchannel lnie'lnlers used at their assembly and being independent. of 10 the temperature variations.

WILLIAM J. PFLAUM.

10 REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 5 Number Name Date 1,845,756 LaMar Feb, 16, 1932 1,860,313 LaMar May 24, 1932 1,861,744 Johnson June 7, 1932 1,907,739 Clark May 9, 1933 1,950,489 Glowack Mar. 13, 1934 2,036,177

LaMar Mar. 31, 1936 

